Less than 6 months after launching, online music streaming upstart Spotify has reached an important milestone: 1m users. Approximately 250,000 of those users are located in the UK.

And Spotify is making progress on the business side too: it has signed up some big ad agencies who are trying out its new ad targeting platform.

The one millionth user registration came at 19:50 GMT on March 1 according to a post on Spotify’s blog which reads:

Our user growth has been amazing since we launched back in October, in
particular the past few weeks have been phenomenal and growth continues
to pick up speed. We can only thank our users who have been great at
spreading the word for us and we look forward to our next big
milestone.

By the looks of it, future milestones will probably be commercial in nature too.

NMA recently reported that MEC, Starcom, Universal Mccann and Zed Media have signed on to use Spotify’s ad targeting platform. Spotify plays a maximum of one 45 second ad every 20 minutes and will also be rolling out demographic targeting options in the future.

So is Spotify an iTunes killer as some have suggested?

Spotify is still only available in 6 countries – the UK, Sweden, Spain, France, Norway and Finland – so it’s not competing yet on the global stage. But the service’s growing popularity is evident and perhaps the best indicator of this is the fact that an ecosystem of websites is being built around Spotify.

ShareMyPlaylists.com, for example, is a new UK-based website that enables Spotify users to share their playlists and discover new music by perusing the playlists of others.

Founded by Spotify user Kieron Donoghue, ShareMyPlaylists.com makes playlists searchable by the keywords used in song descriptions and also allows users to upload custom artwork for their playlists. According to Donoghue, “ShareMyPlaylists.com is a new service mainly aimed at the UK audience and those that prefer a UK slant to their musical choices. We believe that this service will really encourage our visitors, both here and abroad, to share and discover great new music.

ShareMyPlaylists.com joins other Spotify playlist sharing services such as Spotwify and spotiSHARE. There’s also a Firefox Spotify search add-on.

The fact that such services are springing up is a good sign for Spotify. As we have seen with services like Facebook and Twitter, third-party developers can be a real boon to a website’s popularity and success.

As Spotify (hopefully) expands its reach internationally, expect more of these services to be created, helping propel Spotify’s appeal and growth even further.